This invention relates to a dilatation catheter and more particularly to a dilatation catheter construction of particular utility as a monorail dilatation catheter.
Monorail dilatation catheters are becoming increasingly popular in angioplasty procedures because, unlike over-the-wire catheters that require guide wire extenders to perform a catheter exchange, the monorail dilatation catheter construction enables one monorail dilatation catheter to be exchanged readily for another. U.S. Pat. No. 4,762,129 to Bonzel discloses one such catheter having a guide wire lumen only at the distal segment of the catheter, for coupling the catheter and the guide wire together. The guide wire tube extends through the balloon, from the distal end of the catheter to a point proximal to the balloon. Rapid exchange and manipulation of the dilatation catheter is facilitated because the catheter segment in contact with the surface of the guide wire is only as long as the balloon.
Although conventional monorail-type catheters allow rapid catheter exchange, they tend to lack stiffness along their shaft length proximal to the exchange joint, at which point, the catheter gains the benefit of the guide wire to impart stiffness to the catheter. This lack of stiffness along the proximal portion of the catheter makes it difficult to advance the catheter through the body passageway. Bonzel addresses this problem, in part, by providing an integral stabilizing means that extends from the catheter""s proximal end, through the inflation lumen, to the distal end of the balloon.
The use of a stiffening wire (or mandrel) has also been proposed in a monorail catheter to provide controlled stiffness where needed without diminishing flexibility in the distal section of the catheter. Such stiffening wires, however, can buckle under compressive loads and present a potential risk of perforating the catheter wall.
The invention provides an improved monorail dilatation catheter which incorporates a stiffening wire wherein the likelihood of buckling and/or perforation of the catheter shaft is substantially reduced if not eliminated.
Another feature of the invention is applicable to all balloon catheters containing guide wire lumens, for example, both over-the-wire and rapid exchange (monorail) catheters. In such catheters, the guide wire lumen is normally flushed prior to use with a saline/heparin mixture to prevent blood coagulation in the lumen. The guide wire lumen must be large enough to permit free movement of the catheter relative to the guide wire. The larger the gap between the guide wire lumen and the guide wire, the freer the movement, but a smaller gap reduces the catheter profile in the distal region of the catheter, thus facilitating introducing the catheter across the stenosis.
U.S. Pat. No. 5,209,728 to Kraus et al. addresses the problem of having blood enter the catheter, and discloses a catheter provided with a tip member adapted to slidably receive a specially formed guide wire, so as to ensure a liquid-tight seal between the catheter and guide wire. The liquid-tight seal is formed by bringing the inner surface of the catheter sufficiently close to the outer surface of the guide wire. Consequently, the inflation fluid is retained within the catheter, and blood is kept out of the catheter.
However, as is typically the case with over-the-wire catheters, a reduced space between the catheter and the guide wire restricts the clear movement of the guide wire relative to the catheter. Such resistance increases the tendency of the catheter to buckle when the operator attempts to advance the catheter through the body passageway. It would, therefore, be desirable to provide a flexible dilatation catheter having a stiffening wire adapted to impart stiffness to the catheter to prevent buckling as it is manipulated through the body passageway. It would also be desirable to provide such a catheter that limits the amount of blood that enters the catheter, while at the same time, facilitates the free movement of the guide wire with respect to the catheter.
The invention further provides a balloon catheter which is movable with respect to a guide wire, wherein the profile of the distal region of the catheter is reduced without a sacrifice in freedom of movement of the catheter relative to the guide wire.
The present invention is directed towards a dilatation catheter which comprises an elongated catheter shaft, a guide wire tube and an angioplasty balloon. In conventional fashion, the distal end of the balloon is attached to the distal portion of the guide wire tube and the proximal portion of the balloon is attached to the distal portion of the catheter shaft. The first aspect of the invention is directed towards positioning a stiffening wire having a large diameter proximal portion and a small diameter distal portion, within the catheter shaft. The stiffening wire is attached to the inner wall of the catheter shaft at a plurality of points along its length, thereby providing strength to the proximal portion of the catheter, without compromising the size of the inflation/deflation lumen.
The second feature of the invention is applicable to any catheter that includes a guide wire lumen, such as an over-the-wire catheter or a rapid exchange or monorail catheter. According to this feature of the invention, a guide wire lumen is provided with a relatively large gap between the guide wire and the inner surface of the guide wire tube. The distal extremity of the guide wire tube is decreased in size for a short distance. The diameter of this decreased distal extremity approximates the diameter of the guide wire, thereby, substantially reducing the amount of blood that can enter the guide wire lumen. The large diameter portion of the guide wire lumen contains a saline/heparin mix which, because it is less viscous than blood, tends to flow into the gap within the small diameter lumen portion to reduce blood coagulation in that portion and thereby reduce the risk of xe2x80x9cseizing.xe2x80x9d The relative movement between the balloon catheter and the wire creates a wiping action which keeps the wire clean.
The outer diameter of the distal extremity of the guide wire tube is also reduced or tapered. As a result of this taper, the catheter profile in the distal region of the catheter is reduced, facilitating passage of the catheter across a stenosis. As a result of the tapered guide wire tube, the profile of the distal portion of the balloon is appreciably decreased when the balloon is in its collapsed state. This further facilitates positioning the balloon across a stenosis.